This invention relates generally to electronically controlled fuel injected engines and, more particularly, to controlling fuel injection signals during certain engine operating conditions such as acceleration or deceleration wherein one or more injections of fuel (shots) associated with a multi-injection fuel injection event may be disabled to better control engine exhaust emissions.
Electronically controlled direct fuel injection devices such as electronically controlled fuel injectors are well known in the art including both hydraulically actuated electronically controlled fuel injectors as well as mechanically actuated electronically controlled fuel injectors. Electronically controlled fuel injectors typically inject fuel into a specific engine cylinder as a function of an electronic fuel injection signal received from an electronic fuel injection control device (controller) or system. These signals include waveforms that are indicative of a desired injection rate as well as the desired timing and quantity of fuel to be injected into the cylinders.
Emission regulations pertaining to engine exhaust emissions are becoming more restrictive throughout the world including, for example, restrictions on the emission of hydrocarbons, carbon monoxide, the release of particulates, and the release of nitrogen oxides (NOx). Tailoring the electronic fuel injection current signal waveform and the resulting number of injections and the injection rate of fuel to a combustion chamber during a combustion cycle of the cylinder, as well as the quantity and timing of such fuel injections, is one way to improve emissions and meet higher emissions standards. As a result, multiple fuel injection techniques, wherein the electronic fuel injection signal waveform comprises a plurality of distinct fuel injection signals, have been utilized to modify the burn characteristics of the combustion process in an attempt to reduce emission and noise levels. Multiple fuel injections typically involve splitting the total fuel delivery to the cylinder during a particular injection event into separate fuel injections, such as a pilot injection, a main injection, and an anchor injection, where three injections of fuel (a three shot injection) are desired. Each of these injections may also be referred to generally as a shot, and the term shot as used in the art may also refer to the actual fuel injection or to the command current signal (electronic fuel injection current signal), also referred to simply as a fuel injection signal, to a fuel injector indicative of an injection or delivery of fuel to the engine. At different engine operating conditions, it may be necessary to use different injection strategies in order to achieve both desired engine performance and emissions control.
For example, multiple fuel injection techniques may be utilized at engine operating conditions, including low engine speed and low engine load, while other techniques may be utilized at different engine operating conditions. In the past, the controllability of a multiple fuel injection or split injection event has been somewhat restricted by mechanical and other limitations associated with the particular types of injectors utilized. Even with more advanced electronically controlled injectors, during certain engine operating conditions, it is sometimes difficult to accurately control fuel delivery.
As used throughout this disclosure, an xe2x80x9cinjection eventxe2x80x9d is defined as the injections that occur in a particular cylinder or combustion chamber during one cycle of the engine (xe2x80x9ccylinder cyclexe2x80x9d). For example, one cycle of a four stroke engine for a particular cylinder, includes an intake, compression, expansion, and exhaust stroke. Therefore, the injection event/cylinder cycle in a four stroke engine includes the number of injections, or shots, that occur in a cylinder during the four strokes of the piston. As used in the art, and throughout this disclosure, an xe2x80x9cengine operating cyclexe2x80x9d includes the individual cylinder cycles for the cylinders included therein. For example, an engine operating cycle for a six cylinder engine will include six individual cylinder cycles, one for each of the cylinders of the engine (with each cylinder cycle having four strokes, for a total of 24 strokes). Generally, the cylinder cycles overlap, so that the beginning of the next successive cylinder cycle of a particular cylinder might begin prior to the completion of the beginning of the next engine operating cycle. The term xe2x80x9cshotxe2x80x9d as used in the art may also refer to the actual fuel injection or to the command electronic fuel injection current signal (electronic fuel injection current signal), also referred to simply as a fuel injection signal, to a direct fuel injection device, fuel injector or other fuel actuation device indicative of an injection or delivery of fuel to the engine.
U.S. Pat. No. 5,884,602 to Friedrich et al., describes a direct fuel injection compression ignition engine and a process for determining a pilot injection and calculating pilot and main injection fuel quantities. The ""602 patent describes computing a total quantity of fuel to be injected into a cylinder, then determining if a pilot injection will be injected and if so, the quantity of fuel to be injected during the pilot injection, then determining a second (main) injection based on the difference between these values. The method described in the ""602 patent while balancing torque, does not address concerns of changing engine conditions wherein the timing and/or fuel quantity of the main shot will be varied when a pilot shot is eliminated. The three-shot multiple injection event as set out in this disclosure also provides improved engine exhaust emissions while reducing fuel consumption of the engine.
Desired engine performance is not always achieved using three-shot multiple fuel injections or even two-shot (split) multiple injections at all engine speeds and engine load conditions due to a variety of reasons, including limitations on the different types of achievable injection waveform types, the amount of fuel injected during the separate fuel injections, the timing of injections during the particular injection event, the timing sequence between the injections, and how closely spaced injections influence each other. As a result, problems such as injecting fuel too rapidly within a given injection event and/or allowing fuel to be injected beyond a desired stopping point can adversely affect emission outputs and fuel economy.
In a system in which multiple injections and different injection signal waveforms are achievable, it is desirable to control and deliver any number of separate fuel injections to a particular cylinder so as to minimize emissions and fuel consumption based upon the operating conditions of the engine at that particular point in time, e.g. changes in speed, load, or ambient conditions. This may include splitting the fuel injection into two or more separate fuel shots during a particular injection event, providing larger fuel quantities in the pilot shot, advancing the pilot shot during the injection event, and adjusting the timing between the various multiple fuel injection shots in order to achieve desired emissions and desired fuel consumption. In some situations, it is also desirable to rate shape the front end of the fuel delivery to the cylinder to control the burn characteristics of the particular fuel being utilized. Further, in some situations the particular shot duration or the fuel quantity may be so small that it is not practical to inject the particular shot.
By way of example, during certain acceleration events, not all of the fuel delivered to the engine in the distinct fuel shots of a multi-shot fuel injection event is combusted for a variety of reasons. In one such event where a turbo charger is used, during an acceleration event the air mass delivered to the engine is less because the turbo charger device associated with the engine has to spin up to deliver a greater quantity of air corresponding to the increase in the fuel. When a rich fuel mixture is introduced into the cylinder, more fuel is likely to contact the cylinder walls than with a comparatively leaner fuel mixture. Because a cylinder""s walls are typically cooler in comparison to the interior of the cylinder, the fuel does not combust but instead mixes with the cylinder wall lubricating oil. This fuel deteriorates the lubricating quality of the engine oil, and adversely impacts the fuel efficiency of the engine. Furthermore, such uncombusted fuel may be emitted in the form of hydrocarbons, which are a pollutant and therefore an undesirable component of an engine""s emissions.
Further during an acceleration event, the time window available for fuel injection events may decrease. It becomes more difficult to inject multiple shots into a shrinking time window for a cylinder as engine speed increases. Rapidly changing engine speed can cause timing errors for all shots and in particular for shots that are placed at a particular piston position (crank angle). However, this is especially applicable to the anchor shot since it occurs a time delay after the main shot. As a result, the time interval between shots, or the time difference between the end of one fuel shot in a particular fuel injection event and the beginning of a subsequent fuel shot in the same fuel injection event, decreases. Therefore, it becomes increasingly important to deliver the individual fuel shots accurately as the timing between fuel shots becomes shorter.
In a deceleration event, on the other hand, the amount of fuel delivered in a fuel injection event decreases. As the amount of fuel decreases, it becomes increasingly difficult to physically partition the fuel into distinct fuel shots. For small enough amounts of fuel, the improperly partitioned amounts of fuel may result in improper or undesirable performance, efficiency, and emissions of the engine. Further during a deceleration event, the time duration of each fuel injection may increase. As discussed for acceleration above, the time to angle conversion for the individual fuel shots may be inaccurate when the speed of the engine is changing. As a result, the inaccurate (or offset) fuel injection events may detrimentally impact the engine""s performance, efficiency, and emissions during a deceleration event.
It is therefore desirable to provide an apparatus and method to control the delivery of fuel to an engine to control emissions during acceleration and deceleration. Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, an control system and method are disclosed for controlling a fuel injection control system of a direct injection internal combustion engine, capable of issuing a pilot and a main injection during fuel injection into an engine cylinder, determining whether a pilot injection is enabled or disabled for each of the plurality of direct injection devices for each engine operation cycle, and modifying a corresponding main injection timing at least on the basis of the pilot injection determination.
Particularly, the fuel injection control system may include a plurality of direct fuel injection devices operable to deliver partitioned separate injections of fuel directly into corresponding combustion chambers of the internal combustion engine. The control system is operable on the basis of engine operating parameters to control operation of the direct fuel injection devices, and to determine the partitioned separate injections of fuel including a pilot injection fuel quantity, a main injection fuel quantity, an anchor injection fuel quantity, a pilot injection timing and duration, a main injection timing and duration, and an anchor injection timing and duration. The fuel injection control system provides these parameters as fuel injection signal to produce the partitioned separate injections of fuel.
The fuel injection control system is generally adapted to determine if a change in engine conditions has occurred, and on the basis of such determination to determine whether the pilot injection is enabled or disabled. The fuel injection control system is further adapted to dynamically modify the main injection timing at least on the basis of the pilot injection determination.
Another aspect of the present invention describes a method and apparatus for controlling a fuel injection control system to partition fuel output delivery of the fuel injection control system to a plurality of direct fuel injection devices which determines whether a pilot injection is enabled or disabled for each of the plurality of direct injection devices for each engine operation cycle; and modifies a corresponding main injection timing at least on the basis of the pilot injection determination.